1. Field of the Invention
The present invention relates to a cutting wheel for a liquid crystal display panel, and more particularly, to a cutting wheel for a liquid crystal display panel for dividing liquid crystal display panels fabricated on a large-sized glass substrate into individual unit panels by cutting.
2. Discussion of the Related Art
Generally, a liquid crystal display (hereinafter abbreviated LCD) is a display apparatus enabling display of images by supplying liquid crystal cells arranged in a matrix with data signals according to image information to control light transmittance of the respective liquid crystal cells.
LCDs are fabricated by forming thin film transistor (hereinafter abbreviated TFT) array substrates on a large-sized first mother substrate and color filter (hereinafter abbreviated CF) substrates on a second mother substrate and bonding the two mother substrates to each other, thereby fabricating multiple unit liquid crystal display panels simultaneously to improve yield. Hence, LCDs require cutting the bonded mother substrates into a plurality of unit panels.
The cutting process for the unit panels is generally carried out by forming a cutting groove on a surface of the mother substrate using a wheel having a hardness that is greater than that of glass and making a crack propagate along the cutting groove. The cutting process of the unit panel in such an LCD is explained by referring to the attached drawings in detail as follows.
FIG. 1 illustrates a schematic layout of a unit liquid crystal display panel prepared by bonding TFT array and CF substrates to each other.
Referring to FIG. 1, a liquid crystal display panel 10 includes an image display part 13 having liquid crystal cells arranged in a matrix, a gate pad part 14 connected to gate lines of the image display part 13, and a data pad part 15 connected to data lines the image display part 13. In this case, the gate and data pad parts 14 and 15 are formed in a peripheral area of a TFT array substrate 1 which is not overlapped with a CF substrate 2. The gate pad part 14 supplies the gate lines of the image display part 13 with scan signals supplied from a gate driver integrated circuit, while the data pad part 15 supplies the data lines of the image display part 13 with image information supplied from a data driver integrated circuit.
The data and gate lines to which the image information and scan signals are applied respectively cross each other on the TFT array substrate 1 of the image display part 13. At the crossings of the gate and data lines, thin film transistors (not shown) are formed for switching signals to liquid crystal cells. Pixel electrodes are connected to the thin film transistors respectively to apply electric fields to the liquid crystal cells. A passivation layer (not shown) is formed on an entire surface to protect the data lines, gate lines, thin film transistors, and electrodes.
Color filters (not shown) are formed by coating and are separated by a black matrix and a transparent common electrode (not shown) on the CF substrate 2. The common electrode serves as a counter electrode to the pixel electrode on the TFT array substrate 1.
The above-constructed TFT array and CF substrates 1 and 2 are provided with a cell gap therebetween making the substrates 1 and 2 face each other by a uniform distance. The substrates 1 and 2 are bonded to each other by a sealant (not shown) formed at a periphery of the image display part 13, and a liquid crystal layer (not shown) in a space between the TFT array and CF substrates 1 and 2.
FIG. 2 illustrates a cross-sectional view of first and second mother substrates bonded to each other to form a plurality of unit liquid crystal display panels. A plurality of TFT array substrates 1 and a corresponding plurality of CF substrates 2 are formed on the first and second mother substrates, respectively.
Referring to FIG. 2, unit liquid crystal display panels are formed so that one side of each TFT array substrate 1 extends beyond a side of the corresponding CF substrate 2. This is because the gate and data pad parts 14 and 15 are formed on a periphery of the TFT array substrate 1 in an area not overlapped with the corresponding CF substrate 2.
Therefore, an area between adjacent CF substrates 2 on the second mother substrate 30 is as wide as a first dummy area 31 that corresponds to an area of the extension of the respective TFT array substrate on the first mother substrate 20.
Moreover, the unit liquid crystal display panels are arranged properly for a maximum use of the first and second mother substrates 20 and 30. Generally, the unit liquid crystal display panels are formed to be spaced apart from each other as wide as second dummy areas 32, respectively. Third dummy areas 21 are formed at edges of the first and second mother substrates 20 and 30 for a process margin.
After the first mother substrate 20 having the TFT array substrates 1 has been bonded to the second mother substrate 30 having the CF substrates 2, liquid crystal display panels are cut individually. In this case, the first dummy area 31, the second dummy areas 32, and the third dummy areas 21 are removed simultaneously.
FIGS. 3A and 3B illustrate front and side views of a cutting wheel used in cutting liquid crystal display panels.
Referring to FIGS. 3A and 3B, a penetrating hole 41 is formed at a center of a circular cutting wheel 40 to receive a support spindle (not shown), and a sharp blade 42 is formed along an edge of the cutting wheel 40 by grinding front and back faces of the cutting wheel 40.
The cutting wheel 40 rotates and is brought into close contact with a liquid crystal display panel to form a groove having a predetermined depth. After the groove has been formed in the liquid crystal display panel, a crack propagates downward through an applied external impact to cut the liquid crystal display panel.
However, the above-constructed cutting wheel 40 is vulnerable to slipping, which can result in an abnormal groove on the liquid crystal display panel and an inability to control precisely the propagating direction of the cracking and having a required high pressure for adherence between the cutting wheel 40 and liquid crystal display panel to form the groove having a designed depth.
FIGS. 4A and 4B illustrate front and side views of another cutting wheel used in cutting liquid crystal display panels.
Referring to FIGS. 4A and 4B, a penetrating hole 51 is formed at a center of a circular cutting wheel 50 to receive a support spindle (not shown), and a plurality of sharp blades 52 are formed along an edge of the cutting wheel 50 to be spaced apart by a uniform interval to have an uneven or serrated structure.
The cutting wheel 50 shown in FIGS. 4A and 4B rotates and is brought into close contact with a liquid crystal display panel to form a groove having a predetermined depth by applying a uniform pressure thereto, like the other cutting wheel 40 in FIGS. 3A and 3B.
Compared to the cutting wheel 40 shown in FIGS. 3A and 3B, the cutting wheel 50 shown in FIGS. 4A and 4B uses the uneven-structured blades 52 to prohibit slipping on the liquid crystal display panel to prevent the formation of an abnormal groove. Moreover, the cutting wheel 50, which comes into tight contact with the liquid crystal display panel while rotating, gives an concentrated impact on the liquid crystal display panel to force the propagation of the crack in a uniform direction. The liquid crystal display panel can be cut even if the pressure making the cutting wheel 50 adhere closely to the liquid crystal display panel is lower than that of the previous cutting wheel 40 shown in FIGS. 3A and 3B.
Thus, the cutting wheel 50 shown in FIGS. 4A and 4B is more advantageous than the previous cutting wheel 40 in FIGS. 3A and 3B. However, the protruding blades 52 are vulnerable to breakage. When particles such as glass are attached to the groove, a normal groove fails to be formed. Hence, the wheel should be changed frequently, thereby reducing productivity as well as increasing production cost due to purchasing costs of new wheels.
Moreover, when the wheel is generally manufactured with tungsten carbide (WC), abrasion of the wheel requires the replacement of wheel after the formation of about 200 m of grooves on a plurality of the liquid crystal display panels. Furthermore, even if the wheel is made of diamond, which has hardness higher than that of tungsten carbide, and the pressure or speed of the wheel is adjusted, the endurance of the wheel is just extended to about 600 m. Such a short endurance of the wheel requires frequent replacements, thereby reducing productivity as well as increasing production cost.